Georgetown U is another Jesuit university – it is about 50% non-Catholic (and maybe surprisingly? - about 15% Jewish second cite).
GU itself is pretty cagey with the numbers (first cite) but I’ve read 50% undergrad non-Catholic elsewhere too
Which may have to do with GU being in a major metropolitian. You decide to go to BYU or ND, not alot of folks think I’d like to go to school in Provo or South Bend. OTOH you could think I’d like to go to school in DC …
Here is a course syllabus prepared for the Center for the Study of Religion and American Culture in '97 that says 90% of the undergrads at ND are from “Catholic backgrounds”: